Liquid cooled shock absorber

ABSTRACT

A liquid cooled shock absorber unit for a vehicle having an outer cylinder surrounding a shock absorber cartridge forming an annular chamber connected to a source of liquid coolant through a plurality of coolant delivery tubes extending through the annular chamber so as to provide an even circulation of the coolant fluid through the annular chamber and to act as reinforcing strengthening members for the unit. The shock absorber unit is connected in a liquid cooling system separate from the vehicle engine cooling system.

FIELD OF THE INVENTION

This invention relates to liquid cooled tubular shock absorbers and moreparticularly, but not exclusively, to shock absorbers of the hydraulic,gas, or friction type for use in road or rail vehicles, or aircraft.Although not limited thereto, the present invention has particularadvantageous application to gas filled shock absorbers of the Bilsteingas type McPherson strut cartridge and the De Carbon principle struts orshock absorbers.

BACKGROUND OF THE INVENTION

A well known problem associated with telescopic shock absorbersemploying a damping piston reciprocating in a cylinder filled with adamping gas and/or fluid is the temperature dependent dampingcharacteristics of the shock absorber.

The capacity of such shock absorbers to operate efficiently is limitedin certain conditions of operation by their inability to dissipate heatresulting from fluid friction converting the undesirable kinetic energyof the vibrating mass into heat causing thermal overloading.

Generally an increase in the temperature of the damping fluid adverselyaffects the damping characteristics of the shock absorber. When avehicle travels over rough terrain or on a racing circuit the rapidreciprocative axial movement of the damping piston causes thetemperature of the damping fluid to rise rapidly and this can beexacerbated when the ambient temperature is relatively high and thevehicle is being operated at high speed.

U.S. Pat. No. 4,616,810 discloses a liquid cooled shock absorberemploying a jacket which surrounds the damping chamber of the shockabsorber and forms an annular outer chamber. Cooling fluid enters theannular chamber through a narrow, axially extending inlet passage openat the lower end of the annular chamber to allow circulation of thefluid around the remaining main portion of the annular chamber andthence through an outlet connection. The annular outer chamber isconnected for fluid communication with the cooling system of the vehicleengine.

The shock absorber of this patent suffers from the disadvantages of lackof uniform distribution of the cooling liquid around the shock absorbercartridge and the lack of strength in the system in that the jacket andits shock absorber cartridge are subject to distortion due to theunequal cooling, and that being linked into the engine cooling systemthe temperatures therein required for efficient running of the vehicleengine are in the region of 80° C. to 100° C. In this situation withtemperatures at the shock absorber in the vicinity of 100° C. thestrength of the shock absorber drops by approximately one third of itsstatic strength.

It is an object of the present invention to stabilize the temperature ofa shock absorber for consistent and efficient damping and to prevent theshock absorber reaching high temperatures over 100° C. which can resultin seal breakdown and high piston and bore wear distortion of the shockabsorber cartridge. As the temperature of the shock absorber increases,the oil viscosity decreases whereby the damping effect is reduced andpiston speeds increase resulting in excessive wear on the piston and itscylinder wall.

It is a further object of the present invention to provide a coolingsystem for a shock absorber incorporating a coolant casing around theshock absorber cartridge which greatly increases the strength of theshock absorber assembly and this is particularly advantageous in motorsport applications.

Yet another object of the present invention is the provision of acooling system for a shock absorber which is independent of the vehicleengine cooling system wherein the engine coolant is too hot in mostcases to maintain optimum operating temperatures for the shock absorbersand obviates any pipeline or shock absorber failure which could causeloss of engine coolant and serious engine damage.

SUMMARY OF THE INVENTION

According to the invention there is provided a shock absorber unit for avehicle comprising a tubular shock absorber encased in an outer cylinderproviding an annular space between the outer surface of the shockabsorber and the inner surface of the outer cylinder, a first closurecap mounted on one end of the outer cylinder and secured to an end ofthe shock absorber, a second closure cap mounted on the other end of theouter cylinder so as to concentrically locate the other end of the shockabsorber and its piston rod, said first closure cap including an annularliquid distribution chamber adapted to be connected to a source ofliquid coolant and having an outlet duct therein separate from theremainder of said annular chamber and open to said annular space, saidannular chamber having connected thereto a plurality of coolant deliverytubes extending substantially the full length of said annular space.

In order to provide additional strength to the unit the delivery tubesengage against the outer surface of the shock absorber and the innersurface of the outer cylinder in a close sliding fit.

According to a further feature of the invention there is provided ashock absorber liquid cooling system comprising a radiator connect tothe outlet of the shock absorber unit of the invention, a reservoirconnected to the radiator and a circulating pump connected between thereservoir and the shock absorber unit through a flow control valve.

The system may have manual or electronic controls for ensuring optimumcontrol of the temperature of the shock absorber unit.

In order that the invention and its manner of performance may be morefully understood, reference will now be made to an embodiment of theinvention as illustrated in the accompanying drawings, in which:

FIG. 1 is a schematic layout of the system of the invention;

FIG. 2 is a part-sectional side elevation of the shock absorber unit ofthe invention; and

FIG. 3 is a sectional plan view of the unit taken along the line 3--3 ofFIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, the coolant circulating system of FIG. 1includes a shock absorber unit 5 of the invention, a radiator 6connected to the outlet 7 of the unit 5, a reservoir 8 connected betweenradiator 6 and a, preferably electrically driven circulating pump 9 inturn connected to the inlet 10 of the unit 5 through a flow controlvalve 11.

The shock absorber unit 5 as illustrated in FIGS. 2 and 3 comprises aknown shock absorber 12 such as a Bilstein (Trade Mark) gas pressuretype absorber. Shock absorber 12 is encased in an outer cylinder 13generally concentric with unit 5 and forming an annular chamber 14surrounding shock absorber 12.

At the upper end of cylinder 13, as shown in FIG. 2 there is secured aclosure cap 15 to which the upper end of shock absorber 12 isscrew-threadedly connected at 16. Closure cap 15 includes an annularliquid distribution chamber 17 having a single outlet duct 18 thereinseparate and remote from the remainder of chamber 17, said duct 18 beingopen at 19 to the upper end of chamber 14 and connected to the outlet 7.

Diametrically opposite outlet 7 there is located on closure cap 15 aninlet 10 in communication with annular distribution chamber 17.

Connected to and depending from annular chamber 17 are a plurality ofcircumferentially spaced liquid coolant distribution tubes 20 extendinginto the annular chamber 14 and terminating adjacent the lower end ofthe chamber 14. Distribution tubes 20 firmly but slidingly engagebetween the outer surface of shock absorber 12 and the inner surface ofcylinder 13 so as to act as reinforcing members and provide stabilityand additional strength to unit 5 which is particularly advantageous inmotor sport applications.

At the lower end of cylinder 13 there is located a cup shaped closurecap 21 which acts to centralize the lower end of shock absorber 12 andhas a centrally located aperture 22 with a suitable guide bush forpiston rod 23 of shock absorber 12. An O-ring sealing member 24 islocated on the inner end of closure cap 21 to prevent passage of coolantfluid from said annular space 14 into the closure cap 21.

By extending distribution tubes 20 into the annular chamber 14 there isensured optimum and uniform circulation of the coolant fluid and lowoperating temperatures of the shock absorber even under heavy loadoperating conditions resulting in a high level of damping efficiency andsuspension control with minimum wear of the shock absorber parts.

Test results on a dyno test bed on the shock absorber system of thepresent invention compared with a conventional non-cooled shock absorberare set out below:

    ______________________________________                                                   Water                     Shock                                               cooled                    absorber                                            shock                     temp.                                               absorber Radiator Reservoir                                                                             without                                  Time       temp.    temp.    temp.   cooling                                  ______________________________________                                        Start-without                                                                            18° C.                                                                          17° C.                                                                          17° C.                                                                         18° C.                            fan on radiator                                                               After 3 mins.                                                                            19° C.                                                                          21° C.                                                                          20° C.                                                                         49° C.                            After 6 mins.                                                                            21° C.                                                                          21° C.                                                                          23° C.                                                                         70° C.                            After 9 mins.                                                                            23° C.                                                                          25° C.                                                                          24° C.                                                                         86° C.                            After 12 mins.                                                                           23° C.                                                                          25° C.                                                                          24° C.                                                                         96° C.                            After 15 mins.                                                                           29° C.                                                                          29° C.                                                                          28° C.                                                                         108° C.                           After 18 mins.                                                                           29° C.                                                                          29° C.                                                                          24° C.                                                                         124° C.                           with fan opera-                                                               ting for 3 mins.                                                              ______________________________________                                    

Reading taken after 26 minutes showed no change in the temperature ofthe water cooled shock absorber of the invention being stabilized at 29°C.

Temperature data compiled during an Australian Alpine Rally held inApril, 1991 on a Mazda GT-X 4WD vehicle fitted with liquid cooled shockabsorbers according to the present invention over a 30 kilometer specialstage noted for being extremely hard on suspension gave the followingCentigrade temperature readings at the radiators of both the front pairof shock absorbers and the rear pair of shock absorbers:

    __________________________________________________________________________    DATA TAKEN FROM START OF SPECIAL STAGE 14 OVER 30                             KILOMETRES TEMPERATURES TAKEN AT RADIATORS. AMBIENT                           TEMP. 22 DEG. C.                                                              __________________________________________________________________________    REC:327                                                                            11:10:13                                                                           FNT                                                                              IN                                                                              30.9                                                                             OUT                                                                              26 REAR                                                                              IN                                                                              27.8                                                                             OUT                                                                              23.9                                      REC:328                                                                            11:10:46                                                                           FNT                                                                              IN                                                                              30.9                                                                             OUT                                                                              27 REAR                                                                              IN                                                                              27.8                                                                             OUT                                                                              24.9                                      REC:329                                                                            11:11:19                                                                           FNT                                                                              IN                                                                              32 OUT                                                                              27 REAR                                                                              IN                                                                              27.8                                                                             OUT                                                                              24.9                                      REC:330                                                                            11:11:51                                                                           FNT                                                                              IN                                                                              32 OUT                                                                              27.8                                                                             REAR                                                                              IN                                                                              28.8                                                                             OUT                                                                              26                                        REC:331                                                                            11:12:24                                                                           FNT                                                                              IN                                                                              32 OUT                                                                              28.8                                                                             REAR                                                                              IN                                                                              28.8                                                                             OUT                                                                              26                                        REC:332                                                                            11:12:57                                                                           FNT                                                                              IN                                                                              32 OUT                                                                              27.8                                                                             REAR                                                                              IN                                                                              28.8                                                                             OUT                                                                              26                                        REC:333                                                                            11:13:30                                                                           FNT                                                                              IN                                                                              32 OUT                                                                              28.8                                                                             REAR                                                                              IN                                                                              28.8                                                                             OUT                                                                              26                                        REC:334                                                                            11:14:4                                                                            FNT                                                                              IN                                                                              32 OUT                                                                              27.8                                                                             REAR                                                                              IN                                                                              28.8                                                                             OUT                                                                              26                                        REC:335                                                                            11:14:36                                                                           FNT                                                                              IN                                                                              32 OUT                                                                              27.8                                                                             REAR                                                                              IN                                                                              28.8                                                                             OUT                                                                              24.9                                      REC:336                                                                            11:15:0                                                                            FNT                                                                              IN                                                                              32 OUT                                                                              27.8                                                                             REAR                                                                              IN                                                                              29.9                                                                             OUT                                                                              24.9                                      REC:337                                                                            11:15:43                                                                           FNT                                                                              IN                                                                              33 OUT                                                                              27.8                                                                             REAR                                                                              IN                                                                              29.9                                                                             OUT                                                                              26                                        REC:338                                                                            11:16:15                                                                           FNT                                                                              IN                                                                              33 OUT                                                                              28.8                                                                             REAR                                                                              IN                                                                              29.9                                                                             OUT                                                                              27                                        RFC.339                                                                            11:16:48                                                                           FNT                                                                              IN                                                                              34.1                                                                             OUT                                                                              28.8                                                                             REAR                                                                              IN                                                                              30.9                                                                             OUT                                                                              27                                        REC:340                                                                            11:17:21                                                                           FNT                                                                              IN                                                                              35.1                                                                             OUT                                                                              29.9                                                                             REAR                                                                              IN                                                                              32 OUT                                                                              27                                        REC:341                                                                            11:17:53                                                                           FNT                                                                              IN                                                                              35.1                                                                             OUT                                                                              28.8                                                                             REAR                                                                              IN                                                                              32 OUT                                                                              27                                        REC:342                                                                            11:18:26                                                                           FNT                                                                              IN                                                                              35.9                                                                             OUT                                                                              29.9                                                                             REAR                                                                              IN                                                                              32 OUT                                                                              27.8                                      REC:343                                                                            11:18:59                                                                           FNT                                                                              IN                                                                              35.1                                                                             OUT                                                                              33 REAR                                                                              IN                                                                              33 OUT                                                                              28.8                                      RFC:344                                                                            11:19:31                                                                           FNT                                                                              IN                                                                              36.9                                                                             OUT                                                                              33 REAR                                                                              IN                                                                              35.1                                                                             OUT                                                                              29.9                                      REC:345                                                                            11:20:5                                                                            FNT                                                                              IN                                                                              37.9                                                                             OUT                                                                              34.1                                                                             REAR                                                                              IN                                                                              35.1                                                                             OUT                                                                              30.9                                      REC:346                                                                            11:20:38                                                                           FNT                                                                              IN                                                                              40.9                                                                             OUT                                                                              35.1                                                                             REAR                                                                              IN                                                                              35.9                                                                             OUT                                                                              30.9                                      REC:347                                                                            11:21:12                                                                           FNT                                                                              IN                                                                              40.9                                                                             OUT                                                                              35.9                                                                             REAR                                                                              IN                                                                              36.9                                                                             OUT                                                                              33                                        REC:348                                                                            11:21:45                                                                           FNT                                                                              IN                                                                              40.9                                                                             OUT                                                                              36.9                                                                             REAR                                                                              IN                                                                              38.9                                                                             OUT                                                                              34.1                                      REC:349                                                                            11:22:18                                                                           FNT                                                                              IN                                                                              42.9                                                                             OUT                                                                              37.9                                                                             REAR                                                                              IN                                                                              38.9                                                                             OUT                                                                              35.1                                      REC:350                                                                            11:22:51                                                                           FNT                                                                              IN                                                                              42.9                                                                             OUT                                                                              37.9                                                                             REAR                                                                              IN                                                                              38.9                                                                             OUT                                                                              33                                        REC:351                                                                            11:23:24                                                                           FNT                                                                              IN                                                                              42.9                                                                             OUT                                                                              36.9                                                                             REAR                                                                              IN                                                                              39.9                                                                             OUT                                                                              34.1                                      REC:352                                                                            11:23:57                                                                           FNT                                                                              IN                                                                              42.9                                                                             OUT                                                                              36.9                                                                             REAR                                                                              IN                                                                              39.9                                                                             OUT                                                                              34.1                                      REC:353                                                                            11:24:30                                                                           FNT                                                                              IN                                                                              42.9                                                                             OUT                                                                              38.9                                                                             REAR                                                                              IN                                                                              39.9                                                                             OUT                                                                              36                                        CAR STOPPED IN CONTROL END OF SPECIAL STAGE                                   REC:354                                                                            11:25:4                                                                            FNT                                                                              IN                                                                              42.9                                                                             OUT                                                                              39.9                                                                             REAR                                                                              IN                                                                              39.9                                                                             OUT                                                                              39.9                                      REC:355                                                                            11:25:37                                                                           FNT                                                                              IN                                                                              42.9                                                                             OUT                                                                              41.9                                                                             REAR                                                                              IN                                                                              40.9                                                                             OUT                                                                              40.9                                      REC:356                                                                            11:26:11                                                                           FNT                                                                              IN                                                                              43.9                                                                             OUT                                                                              42.9                                                                             REAR                                                                              IN                                                                              41.9                                                                             OUT                                                                              41.9                                      REC:357                                                                            11:26:44                                                                           FNT                                                                              IN                                                                              44.9                                                                             OUT                                                                              43.9                                                                             REAR                                                                              IN                                                                              41.9                                                                             OUT                                                                              41.9                                      REC:358                                                                            11:27:17                                                                           FNT                                                                              IN                                                                              45.9                                                                             OUT                                                                              44.9                                                                             REAR                                                                              IN                                                                              42.9                                                                             OUT                                                                              42.9                                      REC:359                                                                            11:27:50                                                                           FNT                                                                              IN                                                                              46.9                                                                             OUT                                                                              44.9                                                                             REAR                                                                              IN                                                                              43.9                                                                             OUT                                                                              44.9                                      REC:360                                                                            11:28:23                                                                           FNT                                                                              IN                                                                              46.9                                                                             OUT                                                                              45.9                                                                             REAR                                                                              IN                                                                              44.9                                                                             OUT                                                                              44.9                                      REC:361                                                                            11:28:56                                                                           FNT                                                                              IN                                                                              47.9                                                                             OUT                                                                              46.9                                                                             REAR                                                                              IN                                                                              45.9                                                                             OUT                                                                              45.9                                      REC:363                                                                            11:30:3                                                                            FNT                                                                              IN                                                                              41.9                                                                             OUT                                                                              36.9                                                                             REAR                                                                              IN                                                                              39.9                                                                             OUT                                                                              35.9*                                     __________________________________________________________________________     *CAR MOVING: TEMPERATURES DROP IMMEDIATELY                               

The temperature readings taken on the shock absorber shafts at the endof special stage 14 for the Mazda GT-X with liquid cooled shockabsorbers were on average 43° C. and stable, whereas on another vehiclewith conventional non-liquid cooled shock absorbers the averagetemperature reading was 150° C. and rising.

The present invention can be advantageously, but not exclusively, usedwith the above-mentioned manufacturers struts or shock absorbers whereinthese types of struts operate in a unique manner whereby the cartridgepiston rod is connected to the base of the strut body with the largersection damper tube acting as the top link. In the case of a rear shockabsorber the same cartridge which is used in the McPherson strut may beinverted and mounted to replace a conventional telescopic shockabsorber.

In the present invention the cooling system is fully dedicated so as todissipate the large amount of heat generated from shock absorber guidebearings and damping forces experienced. Engine coolant is normally toohot to maintain optimum operating temperatures of the shock absorbersand any piping or shock absorber failure could cause loss of enginecoolant and serious engine damage.

It is desirable, but not essential that each front or rear set of shockabsorbers of the present invention in a vehicle be serviced by onededicated coolant system.

The coolant circulation pump and optional electronic controls may bemounted inside a vehicle cabin or engine bay.

I claim:
 1. A shock absorber unit for a vehicle comprising a tubularshock absorber encased in an outer cylinder providing an annular spacebetween an outer surface of the shock absorber and an inner surface ofthe outer cylinder, a first closure cap mounted on one end of the outercylinder and secured to an end of the shock absorber, a second closurecap mounted on the other end of the outer cylinder so as toconcentrically locate the other end of the shock absorber and a pistonrod cooperating therewith, said first closure cap including an annularliquid distribution chamber adapted to be connected to a source ofliquid coolant and having an outlet duct therein separate from aremainder of said annular chamber and open to the annular space, saidannular chamber having connected thereto a plurality of coolant deliverytubes, circumferentially spaced apart in the annular space between theshock absorber and said outer cylinder and extending substantially thefull length of the annular space, and wherein said coolant deliverytubes engage against the outer surface of the shock absorber and theinner surface of the outer cylinder so as to act as reinforcingstrengthening members for said unit.
 2. A shock absorber unit accordingto claim 1 and including a sealing ring located on the inner end of saidsecond closure cap to prevent passage of the liquid coolant from theannular space into said second closure cap.
 3. A shock absorber unitaccording to any one of claims 1 or 2, further comprising a liquidcooling system comprising a radiator connected between the outlet ductof said unit and a coolant liquid reservoir and a coolant liquidcirculating pump connected between the reservoir and the annular liquiddistribution chamber of said unit through a flow control valve.
 4. Ashock absorber unit according to claim 3, wherein the vehicle has avehicle engine cooling system, said liquid cooling system beingindependent of the vehicle engine cooling system.
 5. A shock absorberunit according to claim 3 further including manual or electronic meansto control the circulation of fluid through the liquid cooling system inaccordance with the temperature of the coolant liquid to ensure optimumcontrol of the temperature of the shock absorber unit.
 6. A shockabsorber unit according to claim 3 wherein the liquid cooling systemincludes and services a front set of shock absorber units of thevehicle.
 7. A shock absorber unit according to claim 3 wherein theliquid cooling system includes and services a rear set of shock absorberunits of the vehicle.